Today, machines and systems are controlled by microcomputer-aided control assemblies in which process variables of the technical process, such as movement, pressure, temperature etc., are processed in an open-loop and/or closed-loop control program. The process variables are generally sampled and processed cyclically. At the sampling time, the instantaneous values of the process variables are recorded, and they are passed on for processing. In the time period between the two samples, the open-loop and/or closed-loop control program refers to the instantaneous values during processing steps.
For specific control tasks, it is necessary to generate specific identification signals for a machine or system when threshold values of a process variable are overshot or undershot. Additional comparison and circuit parts in the form of memories are provided for this purpose, in which the instantaneous value of the process variable is continuously compared with the threshold value. An identification signal is generated if the threshold value is crossed in a specific direction, or is in the region between two threshold values. One such comparison and circuit part is required for each process variable to be monitored.
The object of the invention is to provide a cost-effective and technically optimized solution for monitoring the overshooting or undershooting of process variable threshold values in a technical system in which process parameters are sampled cyclically.